This patent application claims priority on a Japanese patent application, 2002-313428 filed on Oct. 28, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electron beam irradiation apparatus, an electron beam exposure apparatus, and a defect detection method. More particularly, the present invention relates to an electron beam irradiation apparatus, an electron beam exposure apparatus, and a defect detection method for detecting a defect of a backscattered electron detector.
2. Description of the Related Art
An electron beam exposure apparatus includes a backscattered electron detector for detecting backscattered electrons scattering when an electron beam is irradiated to a mark on a wafer or a wafer stage. The electron beam exposure apparatus performs calibration of the irradiation position of the electron beam, measurement of pattern width written on the wafer, etc. based on quantity of the backscattered electrons detected by the backscattered electron detector. In the conventional electron beam exposure apparatus, the backscattered electron detector is directly connected to a testing apparatus at the time of the assembly of a body tube for checking acceptability of the backscattered electron detector.
Since the backscattered electron detector is assembled in the body tube with an electron lens and a deflector under subatmospheric pressure, it is difficult to perform periodical test of the detector frequently by the conventional method of directly connecting the testing device. Furthermore, since a skilled labor is needed for performing the test, it is less efficient and a number of processes are also required. Moreover, the electron beam exposure apparatus usually includes a plurality of backscattered electron detectors, and even if one backscattered electron detector fails, the other backscattered electron detectors detect a certain amount of backscattered electrons. Therefore, there is a possibility that a user does not notice the failure of the backscattered electron detector, and continues to use it in the state where the quantity of backscattered electrons is not correctly detectable.
Therefore, it is an object of the present invention to provide an electron beam irradiation apparatus, an electron beam exposure apparatus, and a defect detection method which can solve the foregoing problem. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to a first aspect of the present invention, there is provided an electron beam irradiation apparatus for irradiating an electron beam to an object. The electron beam irradiation apparatus includes: an electron beam generating section for generating an electron beam; a plurality of backscattered electron detectors for detecting backscattered electrons generated when the electron beam is irradiated on a mark; a plurality of attenuation sections for attenuating signal values indicating quantity of backscattered electrons detected by the plurality of backscattered electron detectors; and a defect detecting section for detecting a defect of the plurality of backscattered electron detectors based on the signal values attenuated by the plurality of attenuation sections, with attenuation factors for the plurality of attenuation sections being varied.
The electron beam irradiation apparatus may further include: a plurality of IV converters for converting the quantity of electrons detected by the plurality of backscattered electron detectors in to voltages, and for generating signal values indicating the quantity of the backscattered electrons; and a plurality of amplifiers for amplifying the signal values generated by the plurality of IV converters. The defect detecting section may detect a defect of the plurality of backscattered electron detectors, the plurality of IV converters, and the plurality of amplifiers.
The electron beam irradiation apparatus may further include an ideal value storage section storing thereon an ideal value, which is a signal value indicating the quantity of the backscattered electrons detected by the plurality of backscattered electron detectors when the plurality of backscattered electron detectors are normal. The defect detecting section may detect the defect of the plurality of backscattered electron detectors by comparing the signal values attenuated by the plurality of the attenuation sections with the ideal value stored on the ideal value storage section.
The electron beam irradiation apparatus may further include an attenuated signal adder for adding a signal value attenuated by a first attenuation section of the plurality of attenuation sections, and a signal value attenuated by a second attenuation section of the plurality of attenuation sections. The first attenuation section may attenuate the signal value indicating the quantity of the backscattered electrons detected by a first backscattered electron detector of the plurality of backscattered electron detectors by a first attenuation factor based on control of the defect detecting section. The second attenuation section may attenuate the signal value indicating the quantity of the backscattered electrons detected by a second backscattered electron detector of the plurality of backscattered electron detectors by a second attenuation factor based on control of the defect detecting section. The attenuated signal adder may add the signal value attenuated by the first attenuation section by the first attenuation factor, and the signal value attenuated by the second attenuation section by the second attenuation factor, and supplies the added signal to the defect detecting section. The defect detecting section may detect the defect of at least one of the first backscattered electron detector and the second backscattered electron detector by varying the first attenuation factor and the second attenuation factor.
The electron beam irradiation apparatus may further include: a plurality of detected signal adders for adding signal values indicating the quantity of the backscattered electrons detected by the plurality of backscattered electron detectors; and an attenuated signal adder for adding a signal value attenuated by a first attenuation section of the plurality of attenuation sections, and a signal value attenuated by a second attenuation section of the plurality of attenuation sections. The plurality of backscattered electron detectors may include: a first backscattered electron detector and a second backscattered electron detector disposed across an optical axis of the electron beam; and a third backscattered electron detector and a fourth backscattered electron detector disposed across the optical axis of the electron beam. The plurality of detected signal adders may include: a first detected signal adder for adding a signal value indicating the quantity of the backscattered electrons detected by the first backscattered electron detector, and a signal value indicating the quantity of the backscattered electrons detected by the second backscattered electron detector; and a second detected signal adder for adding a signal value indicating the quantity of the backscattered electrons detected by the third backscattered electron detector, and a signal value indicating the quantity of the backscattered electrons detected by the fourth backscattered electron detector. The plurality of attenuation sections may include: a first attenuation section for attenuating a signal value added by the first detected signal adder by a first attenuation factor; and a second attenuation section for attenuating a signal value added by the second detected signal adder by a second attenuation factor. The attenuated signal adder may add the signal value attenuated by the first attenuation section by the first attenuation factor, and the signal value attenuated by the second attenuation section by the second attenuation factor, and supplies the added signal to the defect detecting section. The defect detecting section may detect defect of at least one of the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector by varying the first attenuation factor and the second attenuation factor.
The electron beam irradiation apparatus may further include: an ideal value storage section storing thereon an ideal value which is a signal value to be supplied from the attenuated signal adder to the defect detecting section when the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector are normal and when each of the first attenuation factor and the second attenuation factor is set to a predetermined attenuation factor; and a permissible value storage section storing thereon a predetermined permissible value used as a judgment criterion of defect detection. The defect detecting section may judge whether a difference between a first detected signal value, which is a signal value supplied from the attenuated signal adder when each of the first attenuation factor and the second attenuation factor is set to the predetermined attenuation factor, and the ideal value stored on the ideal value storage section is within the predetermined permissible value, and the defect detecting section may detect that at least two of the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector are defective when it is measured that the difference between the first detected signal value and the ideal value is not within the predetermined permissible value.
The permissible value storage section may further store another permissible value, which is smaller than the predetermined permissible value. The defect detecting section may judge whether each of a difference between the second detected signal value and the half of the first detected signal value, and a difference between the third detected signal value and the half of the first detected signal value, is within the other permissible value when it is measured that the difference between the first detected signal value and the ideal value is within the predetermined permissible value, and the defect detecting section may detect that the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector are normal when it is judged that each of the difference between the second detected signal value and the half of the first detected signal value, and the difference between the third detected signal value and the half of the first detected signal value, is within the other permissible value. Where the second detected signal value is a signal value supplied from the attenuated signal adder when the first attenuation factor is set to the predetermined attenuation factor and the second attenuation factor is set to another attenuation factor, which is greater than the predetermined attenuation factor, and the third detected signal value is a signal value supplied from the attenuated signal adder when the first attenuation factor is set to the other attenuation factor and the second attenuation factor is set to the predetermined attenuation factor.
The defect detecting section may compare the second detected signal value with the third detected signal value when it is measured that either the difference between the second detected signal value and the half of the first detected signal value, or the difference between the third detected signal value and the half of the first detected signal value, is not within the other permissible value, and the defect detecting section may detect that at least one of the first backscattered electron detector and the second backscattered electron detectors is defective when the second detected signal value is less than the third detected signal value, and the defect detecting section detects that at least one of the third backscattered electron detector or the fourth backscattered electron detectors is defective when the third detected signal value is less than the second detected signal value.
According to a second aspect of the present invention, there is provided a defect detection method of detecting a defect of a backscattered electron detector. The defect detection method includes steps of: detecting backscattered electrons by a plurality of backscattered electron detectors, the backscattered electrons being generated when an electron beam is irradiated on the mark; attenuating signal values indicating quantity of backscattered electrons detected by the plurality of backscattered electron detectors; and detecting a defect of the plurality of backscattered electron detectors based on attenuated signal values, with attenuation factors in the attenuation step being varied.
The defect detection step may include a step of detecting defect of the plurality of backscattered electron detectors by comparing the ideal value, which is a signal value indicating the quantity of the backscattered electrons detected by the plurality of backscattered electron detectors when the plurality of backscattered electron detectors are normal, with the signal value attenuated in the attenuation step.
The attenuation step may include steps of: attenuating a signal value indicating the quantity of the backscattered electrons detected by a first backscattered electron detector of the plurality of backscattered electron detectors by a first attenuation factor; and attenuating a signal value indicating the quantity of the backscattered electrons detected by a second backscattered electron detector of the plurality of backscattered electron detectors by a second attenuation factor. A defect of at least one of the first backscattered electron detector and the second backscattered electron detector may be detected in the defect detection step based on a signal value, which is a summation of the signal value attenuated by the first attenuation factor and the signal value attenuated by the second attenuation factor in the attenuation steps by varying the first attenuation factor and the second attenuation factor.
The backscattered electron detection step may include a step of detecting the backscattered electrons by a first backscattered electron detector and a second backscattered electron detector disposed across an optical axis of the electron beam, and by a third backscattered electron detector and a fourth backscattered electron detector disposed across an optical axis of the electron beam. The attenuation step may include steps of: generating a first attenuation signal value by attenuating the signal value, which is a summation of the signal value indicating the quantity of backscattered electrons detected by the first backscattered electron detector and the signal value indicating the quantity of backscattered electrons detected by the second backscattered electron detector, by a first attenuation factor; and generating a second attenuation signal value by attenuating the signal value, which is a summation of the signal value indicating the quantity of backscattered electrons detected by the third backscattered electron detector and the signal value indicating the quantity of backscattered electrons detected by the fourth backscattered electron detector, by a second attenuation factor. A defect of at least one of the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector may be detected in the defect detection step based on the signal value, which is a summation of the first attenuation signal value and the second attenuation signal value generated in the attenuation step, by varying the first attenuation factor and the second attenuation factor.
The defect detection step may include steps of: judging whether difference between a first detected signal value and an ideal value is within a predetermined permissible value; and detecting that at least two of the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detectors are defective when it is measured that the difference between the first detected signal value and the ideal value is not within the predetermined permissible value. Where, the first detected signal value is a summation of the first attenuation signal value and the second attenuation signal value where each of the first attenuation factor and the second attenuation factor is set to a predetermined attenuation factor, and the ideal value is a summation of the first attenuation signal value and the second attenuation signal value when the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector are normal and each of the first attenuation factor and the second attenuation factor is set to the predetermined attenuation factor.
The defect detection step may include steps of: judging whether each of a difference between a second detected signal value and the half of the first detected signal value, and a difference between a third detected signal value and the half of the first detected signal value, is within another permissible value, which is smaller than the predetermined permissible value, when it is measured that the difference between the first detected signal value and the ideal value is within the predetermined permissible value; and detecting that the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector are normal when it is judged that each of the difference between the second detected signal value and the half of the first detected signal value, and the difference between the third detected signal value and the half of the first detected signal value, is within the other permissible value. Where, the second detected signal value is a summation of the first attenuation signal value and the second attenuation signal value when the first attenuation factor is set to the predetermined attenuation factor and the second attenuation factor is set to another attenuation factor, which is greater than the predetermined attenuation factor, and the third detected signal is a summation of the first attenuation signal value and the second attenuation signal value when the first attenuation factor is set to the other attenuation factor and the second attenuation factor is set to the predetermined attenuation factor.
The defect detection method may further include a step of storing the first detected signal value as the ideal value when it is detected in the defect detection step that the first backscattered electron detector, the second backscattered electron detector, the third backscattered electron detector, and the fourth backscattered electron detector are normal.
The defect detection step may include steps of: comparing the second detected signal value with the third detected signal value when at least either the difference between the second detected signal value and the half of the first detected signal value, or the difference between the third detected signal value and the half of the first detected signal value, is not within the other permissible value; and detecting that at least one of the first backscattered electron detector and the second backscattered electron detector is defective when the second detected signal value is less than the third detected signal value, and detecting that at least one of the third backscattered electron detector and the fourth backscattered electron detector is defective when the third detected signal value is less than the second detected signal value.
According to a first aspect of the present invention, there is provided an electron beam exposure apparatus for exposing a pattern on a wafer by an electron beam. The electron beam exposure apparatus includes: an electron beam generating section for generating an electron beam; a plurality of backscattered electron detectors for detecting backscattered electrons generated when the electron beam is irradiated on a mark; a plurality of attenuation sections for attenuating signal values indicating quantity of backscattered electrons detected by the plurality of backscattered electron detectors; and a defect detecting section for detecting a defect of the plurality of backscattered electron detectors by varying attenuation factors for the plurality of attenuation sections.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above.